Structures are commonly inspected after fabrication to assess the quality of the structure prior to placing the structure into service. During inspection, a structure may be examined to locate and identify anomalies. For example, a structure may be inspected to locate potential flaws that may exist in the material that makes up the structure. Inspection of a structure may also include measuring the size, shape, and orientation of one or more features of the structure to determine whether such features fall within design tolerances. Measurement of certain features may provide an indication of the integrity of the structure or the integrity of a joint between two components that make up the structure.
For example, metallic tubing for carrying fluids is typically inspected to check the quality of the joint between the tube and a fitting that may be mounted on an end of the tube. A fitting may be mechanically joined to a tube end using a swaging process to form a swage joint wherein the walls of the tube end may be outwardly expanded and forced into grooves in the interior circumference of the fitting to effectively interlock the fitting and the tube. The integrity of the swage joint may be assessed by measuring the increase in the inner diameter of the tube end relative to the nominal diameter of the tube in a non-expanded location. If the increased diameter of the tube end is within a predetermined dimensional range, then the swage joint may pass inspection.
Conventional methods for inspecting swage joints include mechanical measurement techniques. One measurement technique includes the use of a bore gauge having opposing telescopic portions. The bore gauge may be inserted into the end of a tube at the location where a fitting is swaged onto the tube. The telescopic portions of the bore gauge may be outwardly extended until the tips of the telescopic portions contact opposite sides of the inner surface of the tube end. The telescopic portions may then be locked into position and the bore gauge may be removed from the tube. The distance across the tips of the telescopic portions may be measured using a second mechanical device such as a caliper to determine the inner diameter of the tube end for comparison to a predetermined dimensional range.
Unfortunately, the accuracy with which the inner diameter of a tube end may be measured using a bore gauge may depend to a large extent on the skill of the technician. For example, accurate measurement of the inner diameter of a tube at a swage joint may depend upon the skill of the technician in accurately positioning the bore gauge such that each one of the opposing telescoping portions contacts the inner surface of the tube at diametrically opposed locations. As may be appreciated, accurate measurement of the inner diameter of a swage joint using a mechanical measurement technique may present repeatability issues from technician to technician.
In addition, mechanical measurement techniques may present challenges in measuring the inner diameter of a swage joint with the required degree of precision on a repeatable basis. For example, in certain applications, assessing the integrity of a swage joint may require measuring the inner diameter with a resolution as low as several thousands of an inch. Furthermore, assessing the integrity of a swage joint may require accurately measuring the inner diameter at multiple locations around the inner circumference and/or at a multiple locations along an axial direction of the swage joint which may present challenges when measuring with a bore gauge.
As can be seen, there exists a need in the art for a system and method of measuring the inner diameter of a tube with a high degree of accuracy on a repeatable basis.